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JavaScript - if...else Statement

While writing a program, there may be a situation when you need to adopt one out of a given set of paths. In such cases, you need to use conditional statements that allow your program to make correct decisions and perform right actions.

JavaScript supports conditional statements which are used to perform different actions based on different conditions. Here we will explain the if..else statement.

JavaScript supports the following forms of if..else statements

if statement

The if statement is the fundamental control statement that allows JavaScript to make decisions and execute statements conditionally.

Syntax

The syntax for a basic if statement is as follows: 

                
                    if (expression){
                      Statement(s) to be executed if expression is true
                   }

Here a JavaScript expression is evaluated. If the resulting value is true, the given statement(s) are executed. If the expression is false, then no statement would be not executed. Most of the times, you will use comparison operators while making decisions.

Example

Try the following example to understand how the if statement works.

<html>
   <body>
      
      <script type="text/javascript">
            var age = 20;
         
            if( age > 18 ){
               document.write("<b>Qualifies for driving</b>");
            }
      </script>
      
      <p>Set the variable to different value and then try...</p>
   </body>
</html>

Output

        Qualifies for driving
        Set the variable to different value and then try...


if...else statement:

The 'if...else' statement is the next form of control statement that allows JavaScript to execute statements in a more controlled way.

Syntax

        if (expression)
        { 
            Statement(s) to be executed if expression is true 
        } 
        else
        { 
            Statement(s) to be executed if expression is false 
        }

Here JavaScript expression is evaluated. If the resulting value is true, the given statement(s) in the ‘if’ block, are executed. If the expression is false, then the given statement(s) in the else block are executed.

Example

Try the following code to learn how to implement an if-else statement in JavaScript.

                <html>
                   <body>
                      <script type="text/javascript">
                            var age = 15;
                         
                            if( age > 18 ){
                               document.write("<b>Qualifies for driving</b>");
                            }
                            else{
                               document.write("<b>Does not qualify for driving</b>");
                            }
                      </script>
                      <p>Set the variable to different value and then try...</p>
                   </body>
                </html>

Output

        Does not qualify for driving
        Set the variable to different value and then try...
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